Investigation of the pore structure and surface properties of polysulfone membrane on the resultant polyamide layer and the performance of the reverse osmosis membrane

Background Polyamide (PA) thin-film composite reverse osmosis (RO) membranes are mainly composed of nonwoven fabric layer, polysulfone (PSF) ultrafiltration support layer, and polyamide separation layer. The structure of PSF membrane plays a decisive role for the properties and morphology of the PA layer. However, the properties and structural parameters of PSF membranes suitable for fabricating high-performance RO membrane are ambiguous, and the relationship between the structure of PSF membrane and the property of PA layer are still unclear. Methods Here, PSF membranes with different cross-sectional structures, pore-size distributions, surface porosity, and hydrophilicity were prepared by introducing PEG with different molecular weight and concentration, which altered the viscosity of the casting solution and the solvent/nonsolvent exchange rate. Based on these PSF membranes, RO membranes were fabricated to investigate the impact of PSF membrane on the structure of PA layer. Significant findings PSF membrane with larger pore-size (> 100 nm) and hydrophobic surface resulted to defects of the PA layer due to the uneven dispersion of the MPD-containing aqueous solution, while PSF membrane with relative high porosity (3–5 %) and hydrophilic surface lead to irregular PA layer originated from excessive penetration of aqueous solution to the PSF membrane. Thus, PSF membranes suitable for the formation of uniform and dense PA thin-layer should have a relatively dense cross-sectional structure, smaller pore-size (40–60 nm) and lower surface porosity (<3 %).